DRILL

摘要

A drill of high machining precision obtained by preventing the problem of a composite material including a hard-to-cut material such as CFRP, i.e. curling of the surface layer and generation of whisker burr (Q) in the backside layer. In a drill having a spiral lead flute (3) of predetermined lead angle ß formed in the outer circumferential surface of the drill body (1), and a cutting edge (5) formed on the tip end face at a point angle a, point lead portions (3a) having a point lead angle ßa of the spiral lead flute set at a fixed value in the range of -10° to +10° smaller than the lead angle ß are formed at the tip head portions (10, 20) of the drill body, an outer circumferential edge portion (5a) of sharp edge profile is formed in the cutting edge (5) by setting an outer circumferential rake angle ? and the cutting edge (5) is made to have a concave curve ridge line.